The present invention relates generally to electrical panels and, more particularly, to an electrical panel that is configurable to be installed as a service entrance panel or a sub-panel.
Electrical panels, breaker boxes, or load centers frequently include a main contactor, switch, or breaker, which electrically isolates a series of load breakers from a utility power input. In the typical utility power input installation, the main contactor selectively connects or disconnects a first hot lead, L1, and a second hot lead, L2, with a respective bus bar, to which the subsequent load breakers are connected. A neutral lead, N, is connected to a neutral bar from which neutral connections are distributed to each of the loads. In addition, a ground connection is established in the load center, for example, by a ground bar connected to a conductive rod inserted into the ground or to a metal wire pipe exiting the site into the ground. The ground bar provides connection points for ground conductors to be distributed to the loads as required. According to wiring standards, the neutral lead, N, from the utility power is connected to the ground connection at a single location within the load center. Thus, in a standard installation a bonding wire may be connected between the neutral bar and the ground bar.
Occasionally, such load centers are configured to receive a secondary input power source, such as from a generator, to provide electrical power to the individual loads in the event of a utility power failure. During interruption of utility power, the generator supplies power to the load center, which the load center distributes to selected circuits of the building. Depending on factors such as the size of the generator, the number of electrical loads, and whether a load is considered critical (i.e., must remain on during a utility power outage), such as a furnace, sump pump, etc., the secondary power source may power all of the electrical loads or only a portion of the loads.
Similar to the utility power input, the generator includes a first hot lead, L1, a second hot lead, L2, and a neutral lead, N. Further, the generator may be separately derived or non-separately derived. In a non-separately derived system, the neutral connection from the generator is not connected to an earth ground and is, therefore, bonded with the neutral connection from the utility supply. A single connection between the neutrals and grounds is established in the service entrance panel, typically between the neutral bar and the ground bar. In a separately derived system, the neutral connection from the generator is connected to a ground at the generator. Because the electrical system may only be connected between neutral and ground at a single point, extra steps must be taken to properly integrate a separately derived generator with utility power. The neutral leads, N, of the utility power and the secondary source must be switched by the transfer switch in addition to the hot leads. Further, the connection between neutral and ground for the utility system must occur prior to the switched connection such that it is removed when the secondary power source is connected and the equipment grounds for the loads are separated from the neutral. Typically the neutral bar and the ground bar are not connected directly in a service entrance panel but rather they are combined into one dual-function terminal bar. This separation is needed in a service entrance transfer panel to keep the neutrals and ground wires separate when switched to the secondary power source as the connection between neutral and ground takes place further upstream towards the power source and cannot occur again in the panel.
A transfer switch is provided to selectively connect the leads from either the utility power source or the secondary power source to the electrical loads. Depending on the application requirements, the transfer switch may be installed directly in the service entrance panel, which is the point of entry for the utility power, or in a separate subpanel. If the transfer switch is in a subpanel, electrical conductors are run from the service to the subpanel to establish an electrical connection with the utility power within the subpanel. In either case, the connection between the utility neutral and ground is established in the service entrance panel. When the transfer switch is in the service entrance panel, the connection must be established prior to the utility neutral lead entering the transfer switch. When the transfer switch is in the sub panel, no ground connection may be made with the utility neutral lead. Despite the different connection requirements, it is desirable to provide a single electrical panel that may be used either in the service entrance panel or in the subpanel.